- Email: [email protected]
Broadband SIW cavity-backed triangular-ring-slotted antenna for Ku-band applications
Accepted Manuscript Regular paper Broadband SIW Cavity-Backed Triangular-Ring-Slotted Antenna for Ku -Band Applications
Arvind Kumar, S. Raghavan PII: DOI: Reference:
S1434-8411(18)30084-0 https://doi.org/10.1016/j.aeue.2018.02.016 AEUE 52243
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
10 January 2018 12 February 2018
Please cite this article as: A. Kumar, S. Raghavan, Broadband SIW Cavity-Backed Triangular-Ring-Slotted Antenna for Ku -Band Applications, International Journal of Electronics and Communications (2018), doi: https://doi.org/
10.1016/j.aeue.2018.02.016
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Broadband SIW Cavity-Backed Triangular-RingSlotted Antenna for Ku-Band Applications Arvind Kumar* and S Raghavan Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620015. [email protected]*
ABSTRACT–In this letter, a broadband substrate integrated waveguide (SIW) cavity-backed triangular-ring-slotted antenna is demonstrated for planar integration. Instead, using a conventional triangular-ring-slot, a modified triangular-ring-slot is employed to achieve a broader bandwidth response. The conventional triangular-ring-slot generates two hybrid-modes in the vicinity of TE110 and TE120 cavity modes owing to strong loading effect in the SIW cavity resonator. The modified-slot helps to tune the individual resonant frequency of these hybrid modes below -10 dB, which leads broadband impedance bandwidth. The antenna is fabricated and tested, and the experimental results show a bandwidth of 2.09 GHz (13.53%) and a gain of 4 dBi over the entire bandwidth. Moreover, antenna exhibits unidirectional radiation characteristics with uniform gain. Keywords: hybrid-modes; planar cavity-backed antenna; slot antenna; substrate integrated waveguide (SIW); wideband 1. INTRODUCTION State-of-the-art substrate integrate waveguide (SIW), which was firstly developed in [1] as a transmission line, has emerged as a promising technology due to its advantages such as low-cost, low-loss, and easy fabrication using PCB (printed-circuit-board) process. In addition, it can be easily integrated with planar circuits. Since then, SIW has been widely implemented in planar cavity-backed antenna designs. The SIW-based slotted cavity-backed antennas have drawn much attention due to their many advantages over conventional bulky metallic counterparts. In general, SIW based antennas are compact in size, low
spurious radiation losses, low-cost, and light-weighted [2-16]. Moreover, such types of antennas are appropriate to be extended in forming array structures with high gain due to following reasons. First, the close SIW configuration provides better isolation among the array elements. Second, the SIW slot radiators can be used as feedline, which can alleviate additional feeding network as well as reduces design complexity. However, the SIW-based slot antennas suffer from typically narrower bandwidth due high-quality factor (Q) of SIW cavity [4]. In the recent years, several techniques have been proposed to improve the bandwidth. For instance, in [5] a shorted-via was inserted just above the slot to generate an additional resonance, which helps to improve the bandwidth up to 3.7%. In [6], substrate removal technique was adopted to enhance the bandwidth. In [7] and [8], the bandwidth was broadened by using the resonances of hybrid cavity modes and multiresonance slots, respectively. In [9], dual-resonant slots are used for dual-resonance. By tuning these resonances in the desired frequency range, melioration in bandwidth was achieved. Many other efforts have been made for bandwidth enhancement like a multilayered SIW cavity-backed structure was investigated in [10]. A hybrid-antenna was developed in [11] for a broadband response, where, a halfmode SIW cavity coupled with a conventional patch is used to enlarge the bandwidth up to 10%. But, the techniques suggested in [10,11] magnify the size of the antenna and design complexity. Furthermore, a cavity-backed slot antenna was loaded with an open-ended cavity was investigated in [12], the bandwidth of the structure was realized up to 23%, but the design was proposed for millimeter-wave applications. In this paper, a study of a slotted SIW based cavity-backed antenna is presented for planar integration. In the proposed design, a modified triangular-ring-slot is used for radiation, which excites two hybrid-modes between TE110 and TE120 cavity modes. By properly attuning these hybrid-modes in the desired frequency range, an improvement of impedance bandwidth was achieved up to 13.89% with moderate gain and unidirectional radiation characteristics. In order to maintain planar configuration, a 50 Ω microstrip feed line is used with a tapered microstrip-to-SIW transition.
Figure 1 Schematic of antenna configuration 2. DESIGN ANALYSIS: DESIGN AND PRINCIPLE 2.1 Antenna Design Configuration To portray the proposed antenna in detail, the schematic of the design is depicted in Fig 1. An SIW structure is created in a single-layered dielectric substrate by implanting metallic via-array (metallic posts) which realize the lateral walls of the SIW [2]. In order to certify the minimum leakage of electromagnetic energy from the gap between two consecutive vias, the diameter (d) and pitch distance (p) of the via is attuned such that it satisfies the prescribed conditions
and
[12](
free-space wavelength at design frequency). The fundamental dimensions of the SIW cavity resonator could be calculated based on the resonant frequency of the dominant mode (TE110) in its equivalent conventional counterpart as given in [14] by applying (1) and (2).
(1) Where,
(2) Here,
is resonant,
is the speed of light in the free space,
is relative permittivity of the dielectric
substrate, and m, n, p’ are positive integers. Finally, SIW cavity dimensions are optimized to wcav = 15.4 mm and lcav = 11.5 mm, so that TE110 and TE120 modes exist at 13.1 and 15.7 GHz as shown in Fig 3. A modified triangular-ring-slot is etched on the top metal cladding of the dielectric substrate. The slot is introduced at a distance of ‘a’ and ‘b’ from one side wall and a top wall of the SIW cavity resonator as shown in Fig 1. The initial perimeter of the ring-slot is estimated as twice of the resonant length corresponding dominant cavity mode. The modified triangular-ring-slot is excited by an integrated waveguide via an inductive window of width ‘wwin’. This integrated waveguide provides extra shielding from spurious radiation losses. TABLE 1 DIMENSIONS OF THE PROPOSED DESIGN Parameters wcav lcav wwin ls l wtap w50
Values (mm) 15.4 11.5 8.6 12.2 10 6.86 4.8
S11, (dB)
0
Parameters lms ltap t a b p d
Values (mm) 6 3.75 0.5 3.7 1.15 1.5 1
Convetional Triangular-Ring slot
-10
-20 Modified Triangular-Ring slot -30 13
14
15 Frequency, (GHz)
16
17
Figure 2 Reflection coefficients (S11) for conventional and modified triangular-ring-slot
400 TE110
Re(Zin) , (ohm)
300
TE120
200 Hybrid modes region
100 0
Re(Z11)_SIW cavity Re(Z11)_convetional triangular-ring slot
-100
Re(Z11)_modified triangular-ring slot -200 10
12
14
16
18
Frequency, (GHz)
Figure 3 Real Input impedance (Z11) plot Furthermore, the feedline is extended by 50Ω microstrip line for testing purpose and tapered microstripto-SIW transition is used for smooth power transmission. The proposed design is optimized by using computer simulation technology (CST) tool, and the optimized antenna parameters are tabulated in Table 1. The volume occupied by the antenna, including transition in terms of
is 0.77
× 1.63
× 0.07
(15.4 mm × 32.7 mm × 1.57 mm). 2.2 Antenna Working Principle The modified triangular-ring-slot induces strong loading effect to the SIW cavity resonator, resultantly, two hybrid-modes get excited in the resonator in nearby proximity. By attuning these hybrid modes, the individual impedance bandwidth gets merged with each other and broadband response is realized as depicted in Fig. 2. The loading effect in the SIW cavity due loading of the conventional triangular-ringslot and the proposed slot is characterized in Fig. 3 with the help of real input impedance plot (Re (Z11)). It can be clearly observed that loading of the proposed slot, severely affects the resonant frequency due to higher-order cavity mode (TE120) whereas, it has a negligible impact on lower-order cavity mode (TE110). In the course of a conventional triangular-ring-slot loaded antenna, the hybrid-mode at 16.47 GHz shifts to 15.7 GHz after introducing modified slot as shown in Fig. 3. Also, Fig. 2 describes the
same. This can be better understood with the help of electric and magnetic field distribution at corresponding modes. The field distributions (electric and magnetic) corresponding to TE110 and TE120 cavity modes are provided in Fig. 4(a), which perturb each other after introducing the proposed slot and generate two hybrid-modes at the frequency of 14.5 and 15.7 GHz frequency as provided in Fig. 4(b). Both electric and magnetic field distributions at the lower-frequency are mostly concentrated along segment (
whereas in the case of higher-frequency, it is mostly concentrated along segment
is symbolized in Fig. 1). Thus, above-mentioned segments predominantly contribute in the
radiation at the corresponding resonant frequency due difference in magnitude and phase of the electric and magnetic field distribution at the opposite side of the slots.
Electric field distribution
Magnetic field distribution (i) 13.1 GHz (TE110)
(ii) 15.7 GHz (TE120) (a)
(i) 14.5 GHz
(ii) 15.7 GHz (b)
Figure 4 Field distributions at the top metal cladding at corresponding frequencies (a) without slot and (b) with slot loading
2.3 Parametric studies To attain a better understanding of broadband impedance matching, a parametric study of some critical parameters is conducted in Figs. 5-9 using CST simulator. To comprehend the effect of a particular parameter, the value of the studied parameter is varied while all other parameters are kept at optimized values. Fig. 5 and 6 show the variation of reflection coefficients (S 11) with a change in parameters ‘ls’ and ‘t’, respectively. Fig 5 shows as the value of ‘ls’ increases, the size of the slot perimeter and the patch is augmented, and as a result, resonances shift towards the lower-frequency. Similarly, vice versa is observed in Fig. 6 as its value enlarged. The inductive window ‘wwin ’ plays a critical role to impedance bandwidth below -10 dB as shown in Fig. 7. Finally, effects of the location of the slot from one side wall and a top wall of the cavity are represented in Fig 8 and 9, respectively. By properly attuning all these critical parameters, the simulated result witnessed that antenna shows a broadband response over 2 GHz ranging from 14.43~16.49 GHz. All studied parameters are symbolically represented in Fig. 1.
ls = 11.8 mm
0
ls = 12.2 mm
S11, (dB)
ls = 12.6 mm -10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 5 Variation of the S11 with change in parameter ‘ls’
t = 0.4 mm t = 0.5 mm t = 0.6 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 6 Variation of the S11 with change in parameter ‘t’
wwin = 7.8 mm
0
wwin = 8.6 mm
S11, (dB)
wwin = 9.4 mm -10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 7 Variation of the S11 with change in parameter ‘wwin’
a = 3.4 mm a = 3.7 mm a = 4.0 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 8 Variation of the S11 with change in parameter ‘a’
b = 0.85 mm b = 1.15 mm b = 1.45 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 9 Variation of the S11 with change in parameter ‘b’
Figure 10 Fabricated antenna prototype 3. FABRICATION AND MEASUREMENTS In order to verify our proposal, the design is prototyped with the help of printed-circuit-board technology on a single-layered Rogers RT/Duroid 5880 substrate (thickness of 1.57 mm, loss tangent of 0.0009 and dielectric constant of 2.2). The photograph of the fabricated antenna is shown in Fig. 10. The simulated and measured reflection coefficient performance of the proposed design is compared in Fig. 11(a), which is mostly in good agreement with each other. The measured result shows that antenna resonates at the frequency of 14.6 GHz and 15.7 GHz. The antenna exhibits a measured impedance bandwidth of 13.53% (2.09 GHz) ranging from 14.43~16.49 GHz, which is close to the simulated bandwidth of 13.89% ranging from 14.13~16.25 GHz. The measured and simulated gain is also equated in Fig. 11(a). The antenna shows uniform gain characteristics for entire operating bandwidth. The measured value of gain at 14.6 GHz and 15.7 is 4.7 dBi and 4.2 dBi, respectively, which higher than previously reported design in [15]. Some degree of inconsistency between simulated and measured results is observed, which
may be due to imperfections in the fabrication and soldering. Furthermore, the simulated radiation and total antenna efficiency are plotted in Fig. 11(b), which is greater than 90 and 80 %, respectively. The simulated and measured radiation patterns (co-polar and cross-polar) in the E and H-plane of the antenna at the frequency of 14.6 GHz and 15.7 are plotted in Fig. 12(a) and (b), respectively. The measured results are once again in good agreement with simulated results. The antenna exhibits unidirectional and almost stable radiation characteristic in boresight direction and it maintains good front-to-back-ratio better than15 dB in each case. Moreover, the proposed antenna has a simple geometry which can be easily rescaled for any range of desired frequency. Therefore, this antenna design can be a suitable choice for the modern wireless communication system operating in
band (12–18 GHz), particularly for broadband applications. The
performance comparison between the proposed work and some previously reported SIW based wideband antennas is summarized in Table 2. The proposed antenna exhibits relatively broader bandwidth while the overall performance is comparable. 8 0
0 -4
-20
Sim. S11 Meas. S11
-8
Sim. Gain Meas. Gain
-30
-12 13
14
15
16
17
Frequency, (GHz)
(a)
100 80 Sim. Rad. Effi. Sim.Tot. Effi.
60 40 13
14
15 Frequency, (GHz)
16
17
Gain, (dBi)
-10
Efficiency (%)
S11, (dB)
4
(b) Figure 11 (a) simulated and measured S11 and gain, and (b) simulated antenna efficiency
Simulated Co-pol. Measured. Co-pol. Simulated Cross-pol. Measured Cross-pol. 90 135
90
0
45
0
135
-10 -20
-20
-30
180
45
-10
-30
0 180
315
225
0
315
225
270
270 (a)
90 135
90
0
45
135
-10
-10
-20
-20
-30
180
0
-30
0 180
315
225
45
315
225
270
0
270 (b)
Figure 12 E and H-plane radiation patterns (a) at 14.6 GHz, and (b) at 15.7 GHz TABLE 2 PERFORMANCE COMPARISON: PROPOSED WORK VS SOME PREVIOUSLY REPORTED WORK Properties Proposed design
Substrate thickness 1.57
-10 dB, (S11) BW (%) 13.53
Peak gain (dBi) 4.7
[2] [7] [8]
0.5 0.78 1.57
1.8 6.3 11.0
5.3 6.0 6.0
0.78 1.57
10 1.4,5.7
7.5 4.8, 6.1
[11] [14] [15]
4. CONCLUSION
Freq band
,
0.78
9.4 3.8 *Microstrip Line (MSL) **
Feeding topology SIW, MSL MSL MSL MSL MSL MSL, SIW MSL
In this paper, a low-profile broadband planar cavity-backed antenna is presented for Ku-band applications. The proposed antenna uses a modified triangular-ting-slot for radiation. The radiation slot is excited by an SIW feed through the inductive window follows 50 Ω microstrip line for planar integration. The modified triangular-ting-slot on the top cladding induces strong loading effect to the SIW cavity, resultantly, two hybrid modes get excited between TE 110 and TE120 cavity modes. The individual bandwidths of these hybrid modes are in close proximity which leads to a broadband response. The antenna exhibits a measured impedance bandwidth of 13.53% ranging from 14.43~16.49 GHz. The proposed design can be easily rescaled to any desired frequency range by altering corresponding dimensions. The total volume occupied by the antenna, including transition in terms of is 0.77
× 1.63
× 0.07 . Moreover, proposed antenna exhibits unidirectional radiation and
uniform gain characteristics about 4 dBi for the entire operating frequency range, which makes it a promising candidate for broadband applications. REFERENCES 1.
Deslandes D, Wu K. Integrated microstrip and rectangular waveguide in planar form. IEEE Microw. Wireless Compon Lett. 2001;11:68–70.
2.
Luo GQ, Hu ZF, Liang Y. Development of low profile cavity backed crossed slot antennas for planar integration. IEEE Trans Antennas Propag. 2009;57:2972–2979.
3.
Liu Y, Chen S, Ren Y, Cheng J, Liu QH. A broadband proximity-coupled dual-polarized microstrip antenna with L-shape backed cavity for X-band applications. AEU-International Journal of Electronics and Communications. 2015 Sep 30;69(9):1226-32.
4.
Kumar A, Raghavan S. Design of a broadband planar cavity-backed circular patch antenna. AEUInternational Journal of Electronics and Communications. 2017 Dec 1;82:413-9.
5.
Yun S, Kim DY, Nam S. Bandwidth enhancement of cavity backed slot antenna using a via-hole above the Slot. IEEE Antenna Wireless Propag Lett. 2012;11:1092–1095.
6.
Yun S, Kim DY, Nam S. Bandwidth and efficiency enhancement of cavity-backed slot antenna using a substrate removal. IEEE Antenna Wireless Propag Lett. 2012;11:1458–1461.
7.
Luo GQ, Hu ZF, Li WJ, Zhang XH, Sun LL, Zheng JF. Bandwidth enhanced low-profile cavitybacked slot antenna by using hybrid SIW cavity modes. IEEE Trans Antennas Propag. 2012:60:1698–1704.
8.
Kumar A, Raghavan S. Wideband slotted substrate integrated waveguide cavity backed antenna for Ku–band application. Microw Opt Technol Lett. 2017;59:1613–1619.
9.
Sievenpiper D, Hsu HP, Riley RM. Low-profile cavity-backed crossed-slot antenna with a singleprobe feed designed for 2.34-GHz satellite radio applications. IEEE Trans. Antennas Propag. 2004;52:873–879.
10.
Yang W, Zhou J. Wideband low profile substrate integrated waveguide cavity backed E-shaped patch antenna. IEEE Antenna Wireless Propag Lett. 2013;1:143–146.
11.
Dashti H, Neshati MH. Development of low-profile patch and semi-circular SIW cavity hybrid antennas. IEEE Trans Antennas Propag. 2014;62:4481–4488.
12.
Xu JF, Chen ZN, Qing XM, Hong W. Bandwidth enhancement for a 60 GHz substrate integrated waveguide fed cavity array antenna on LTCC. IEEE Trans. Antennas Propag. 2011;59:826–832.
13.
Xu F, Wu K. Guided-wave and leakage characteristics of substrate integrated waveguide. IEEE Trans Microwave Theory Tech. 2005;53:66–73
14.
Zhang T, Hong W, Zhang Y, Wu K. Design and analysis of SIW cavity backed dual-band antennas with a dual-mode triangular ring slot. IEEE Trans Antennas Propag. 2014;62:5007–5016.
15.
Mukherjee S, Biswas A, Srivastava KV. Broadband substrate integrated waveguide cavity-backed bow-tie slot antenna. IEEE Antenna Wireless Propag Lett. 2014;13;1152–1155.
Broadband SIW Cavity-Backed TriangularRing-Slotted Antenna for Ku-Band Applications Author-1: (Corresponding Author) Arvind Kumar Dept. Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620 015 [email protected], contact no. 8903228621
Author-2: Singaravelu Raghavan Dept. Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620 015 [email protected]
Arvind Kumar, S. Raghavan PII: DOI: Reference:
S1434-8411(18)30084-0 https://doi.org/10.1016/j.aeue.2018.02.016 AEUE 52243
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
10 January 2018 12 February 2018
Please cite this article as: A. Kumar, S. Raghavan, Broadband SIW Cavity-Backed Triangular-Ring-Slotted Antenna for Ku -Band Applications, International Journal of Electronics and Communications (2018), doi: https://doi.org/
10.1016/j.aeue.2018.02.016
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Broadband SIW Cavity-Backed Triangular-RingSlotted Antenna for Ku-Band Applications Arvind Kumar* and S Raghavan Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620015. [email protected]*
ABSTRACT–In this letter, a broadband substrate integrated waveguide (SIW) cavity-backed triangular-ring-slotted antenna is demonstrated for planar integration. Instead, using a conventional triangular-ring-slot, a modified triangular-ring-slot is employed to achieve a broader bandwidth response. The conventional triangular-ring-slot generates two hybrid-modes in the vicinity of TE110 and TE120 cavity modes owing to strong loading effect in the SIW cavity resonator. The modified-slot helps to tune the individual resonant frequency of these hybrid modes below -10 dB, which leads broadband impedance bandwidth. The antenna is fabricated and tested, and the experimental results show a bandwidth of 2.09 GHz (13.53%) and a gain of 4 dBi over the entire bandwidth. Moreover, antenna exhibits unidirectional radiation characteristics with uniform gain. Keywords: hybrid-modes; planar cavity-backed antenna; slot antenna; substrate integrated waveguide (SIW); wideband 1. INTRODUCTION State-of-the-art substrate integrate waveguide (SIW), which was firstly developed in [1] as a transmission line, has emerged as a promising technology due to its advantages such as low-cost, low-loss, and easy fabrication using PCB (printed-circuit-board) process. In addition, it can be easily integrated with planar circuits. Since then, SIW has been widely implemented in planar cavity-backed antenna designs. The SIW-based slotted cavity-backed antennas have drawn much attention due to their many advantages over conventional bulky metallic counterparts. In general, SIW based antennas are compact in size, low
spurious radiation losses, low-cost, and light-weighted [2-16]. Moreover, such types of antennas are appropriate to be extended in forming array structures with high gain due to following reasons. First, the close SIW configuration provides better isolation among the array elements. Second, the SIW slot radiators can be used as feedline, which can alleviate additional feeding network as well as reduces design complexity. However, the SIW-based slot antennas suffer from typically narrower bandwidth due high-quality factor (Q) of SIW cavity [4]. In the recent years, several techniques have been proposed to improve the bandwidth. For instance, in [5] a shorted-via was inserted just above the slot to generate an additional resonance, which helps to improve the bandwidth up to 3.7%. In [6], substrate removal technique was adopted to enhance the bandwidth. In [7] and [8], the bandwidth was broadened by using the resonances of hybrid cavity modes and multiresonance slots, respectively. In [9], dual-resonant slots are used for dual-resonance. By tuning these resonances in the desired frequency range, melioration in bandwidth was achieved. Many other efforts have been made for bandwidth enhancement like a multilayered SIW cavity-backed structure was investigated in [10]. A hybrid-antenna was developed in [11] for a broadband response, where, a halfmode SIW cavity coupled with a conventional patch is used to enlarge the bandwidth up to 10%. But, the techniques suggested in [10,11] magnify the size of the antenna and design complexity. Furthermore, a cavity-backed slot antenna was loaded with an open-ended cavity was investigated in [12], the bandwidth of the structure was realized up to 23%, but the design was proposed for millimeter-wave applications. In this paper, a study of a slotted SIW based cavity-backed antenna is presented for planar integration. In the proposed design, a modified triangular-ring-slot is used for radiation, which excites two hybrid-modes between TE110 and TE120 cavity modes. By properly attuning these hybrid-modes in the desired frequency range, an improvement of impedance bandwidth was achieved up to 13.89% with moderate gain and unidirectional radiation characteristics. In order to maintain planar configuration, a 50 Ω microstrip feed line is used with a tapered microstrip-to-SIW transition.
Figure 1 Schematic of antenna configuration 2. DESIGN ANALYSIS: DESIGN AND PRINCIPLE 2.1 Antenna Design Configuration To portray the proposed antenna in detail, the schematic of the design is depicted in Fig 1. An SIW structure is created in a single-layered dielectric substrate by implanting metallic via-array (metallic posts) which realize the lateral walls of the SIW [2]. In order to certify the minimum leakage of electromagnetic energy from the gap between two consecutive vias, the diameter (d) and pitch distance (p) of the via is attuned such that it satisfies the prescribed conditions
and
[12](
free-space wavelength at design frequency). The fundamental dimensions of the SIW cavity resonator could be calculated based on the resonant frequency of the dominant mode (TE110) in its equivalent conventional counterpart as given in [14] by applying (1) and (2).
(1) Where,
(2) Here,
is resonant,
is the speed of light in the free space,
is relative permittivity of the dielectric
substrate, and m, n, p’ are positive integers. Finally, SIW cavity dimensions are optimized to wcav = 15.4 mm and lcav = 11.5 mm, so that TE110 and TE120 modes exist at 13.1 and 15.7 GHz as shown in Fig 3. A modified triangular-ring-slot is etched on the top metal cladding of the dielectric substrate. The slot is introduced at a distance of ‘a’ and ‘b’ from one side wall and a top wall of the SIW cavity resonator as shown in Fig 1. The initial perimeter of the ring-slot is estimated as twice of the resonant length corresponding dominant cavity mode. The modified triangular-ring-slot is excited by an integrated waveguide via an inductive window of width ‘wwin’. This integrated waveguide provides extra shielding from spurious radiation losses. TABLE 1 DIMENSIONS OF THE PROPOSED DESIGN Parameters wcav lcav wwin ls l wtap w50
Values (mm) 15.4 11.5 8.6 12.2 10 6.86 4.8
S11, (dB)
0
Parameters lms ltap t a b p d
Values (mm) 6 3.75 0.5 3.7 1.15 1.5 1
Convetional Triangular-Ring slot
-10
-20 Modified Triangular-Ring slot -30 13
14
15 Frequency, (GHz)
16
17
Figure 2 Reflection coefficients (S11) for conventional and modified triangular-ring-slot
400 TE110
Re(Zin) , (ohm)
300
TE120
200 Hybrid modes region
100 0
Re(Z11)_SIW cavity Re(Z11)_convetional triangular-ring slot
-100
Re(Z11)_modified triangular-ring slot -200 10
12
14
16
18
Frequency, (GHz)
Figure 3 Real Input impedance (Z11) plot Furthermore, the feedline is extended by 50Ω microstrip line for testing purpose and tapered microstripto-SIW transition is used for smooth power transmission. The proposed design is optimized by using computer simulation technology (CST) tool, and the optimized antenna parameters are tabulated in Table 1. The volume occupied by the antenna, including transition in terms of
is 0.77
× 1.63
× 0.07
(15.4 mm × 32.7 mm × 1.57 mm). 2.2 Antenna Working Principle The modified triangular-ring-slot induces strong loading effect to the SIW cavity resonator, resultantly, two hybrid-modes get excited in the resonator in nearby proximity. By attuning these hybrid modes, the individual impedance bandwidth gets merged with each other and broadband response is realized as depicted in Fig. 2. The loading effect in the SIW cavity due loading of the conventional triangular-ringslot and the proposed slot is characterized in Fig. 3 with the help of real input impedance plot (Re (Z11)). It can be clearly observed that loading of the proposed slot, severely affects the resonant frequency due to higher-order cavity mode (TE120) whereas, it has a negligible impact on lower-order cavity mode (TE110). In the course of a conventional triangular-ring-slot loaded antenna, the hybrid-mode at 16.47 GHz shifts to 15.7 GHz after introducing modified slot as shown in Fig. 3. Also, Fig. 2 describes the
same. This can be better understood with the help of electric and magnetic field distribution at corresponding modes. The field distributions (electric and magnetic) corresponding to TE110 and TE120 cavity modes are provided in Fig. 4(a), which perturb each other after introducing the proposed slot and generate two hybrid-modes at the frequency of 14.5 and 15.7 GHz frequency as provided in Fig. 4(b). Both electric and magnetic field distributions at the lower-frequency are mostly concentrated along segment (
whereas in the case of higher-frequency, it is mostly concentrated along segment
is symbolized in Fig. 1). Thus, above-mentioned segments predominantly contribute in the
radiation at the corresponding resonant frequency due difference in magnitude and phase of the electric and magnetic field distribution at the opposite side of the slots.
Electric field distribution
Magnetic field distribution (i) 13.1 GHz (TE110)
(ii) 15.7 GHz (TE120) (a)
(i) 14.5 GHz
(ii) 15.7 GHz (b)
Figure 4 Field distributions at the top metal cladding at corresponding frequencies (a) without slot and (b) with slot loading
2.3 Parametric studies To attain a better understanding of broadband impedance matching, a parametric study of some critical parameters is conducted in Figs. 5-9 using CST simulator. To comprehend the effect of a particular parameter, the value of the studied parameter is varied while all other parameters are kept at optimized values. Fig. 5 and 6 show the variation of reflection coefficients (S 11) with a change in parameters ‘ls’ and ‘t’, respectively. Fig 5 shows as the value of ‘ls’ increases, the size of the slot perimeter and the patch is augmented, and as a result, resonances shift towards the lower-frequency. Similarly, vice versa is observed in Fig. 6 as its value enlarged. The inductive window ‘wwin ’ plays a critical role to impedance bandwidth below -10 dB as shown in Fig. 7. Finally, effects of the location of the slot from one side wall and a top wall of the cavity are represented in Fig 8 and 9, respectively. By properly attuning all these critical parameters, the simulated result witnessed that antenna shows a broadband response over 2 GHz ranging from 14.43~16.49 GHz. All studied parameters are symbolically represented in Fig. 1.
ls = 11.8 mm
0
ls = 12.2 mm
S11, (dB)
ls = 12.6 mm -10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 5 Variation of the S11 with change in parameter ‘ls’
t = 0.4 mm t = 0.5 mm t = 0.6 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 6 Variation of the S11 with change in parameter ‘t’
wwin = 7.8 mm
0
wwin = 8.6 mm
S11, (dB)
wwin = 9.4 mm -10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 7 Variation of the S11 with change in parameter ‘wwin’
a = 3.4 mm a = 3.7 mm a = 4.0 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 8 Variation of the S11 with change in parameter ‘a’
b = 0.85 mm b = 1.15 mm b = 1.45 mm
S11, (dB)
0
-10
-20
-30 13
14
15
16
17
Frequency, (GHz)
Figure 9 Variation of the S11 with change in parameter ‘b’
Figure 10 Fabricated antenna prototype 3. FABRICATION AND MEASUREMENTS In order to verify our proposal, the design is prototyped with the help of printed-circuit-board technology on a single-layered Rogers RT/Duroid 5880 substrate (thickness of 1.57 mm, loss tangent of 0.0009 and dielectric constant of 2.2). The photograph of the fabricated antenna is shown in Fig. 10. The simulated and measured reflection coefficient performance of the proposed design is compared in Fig. 11(a), which is mostly in good agreement with each other. The measured result shows that antenna resonates at the frequency of 14.6 GHz and 15.7 GHz. The antenna exhibits a measured impedance bandwidth of 13.53% (2.09 GHz) ranging from 14.43~16.49 GHz, which is close to the simulated bandwidth of 13.89% ranging from 14.13~16.25 GHz. The measured and simulated gain is also equated in Fig. 11(a). The antenna shows uniform gain characteristics for entire operating bandwidth. The measured value of gain at 14.6 GHz and 15.7 is 4.7 dBi and 4.2 dBi, respectively, which higher than previously reported design in [15]. Some degree of inconsistency between simulated and measured results is observed, which
may be due to imperfections in the fabrication and soldering. Furthermore, the simulated radiation and total antenna efficiency are plotted in Fig. 11(b), which is greater than 90 and 80 %, respectively. The simulated and measured radiation patterns (co-polar and cross-polar) in the E and H-plane of the antenna at the frequency of 14.6 GHz and 15.7 are plotted in Fig. 12(a) and (b), respectively. The measured results are once again in good agreement with simulated results. The antenna exhibits unidirectional and almost stable radiation characteristic in boresight direction and it maintains good front-to-back-ratio better than15 dB in each case. Moreover, the proposed antenna has a simple geometry which can be easily rescaled for any range of desired frequency. Therefore, this antenna design can be a suitable choice for the modern wireless communication system operating in
band (12–18 GHz), particularly for broadband applications. The
performance comparison between the proposed work and some previously reported SIW based wideband antennas is summarized in Table 2. The proposed antenna exhibits relatively broader bandwidth while the overall performance is comparable. 8 0
0 -4
-20
Sim. S11 Meas. S11
-8
Sim. Gain Meas. Gain
-30
-12 13
14
15
16
17
Frequency, (GHz)
(a)
100 80 Sim. Rad. Effi. Sim.Tot. Effi.
60 40 13
14
15 Frequency, (GHz)
16
17
Gain, (dBi)
-10
Efficiency (%)
S11, (dB)
4
(b) Figure 11 (a) simulated and measured S11 and gain, and (b) simulated antenna efficiency
Simulated Co-pol. Measured. Co-pol. Simulated Cross-pol. Measured Cross-pol. 90 135
90
0
45
0
135
-10 -20
-20
-30
180
45
-10
-30
0 180
315
225
0
315
225
270
270 (a)
90 135
90
0
45
135
-10
-10
-20
-20
-30
180
0
-30
0 180
315
225
45
315
225
270
0
270 (b)
Figure 12 E and H-plane radiation patterns (a) at 14.6 GHz, and (b) at 15.7 GHz TABLE 2 PERFORMANCE COMPARISON: PROPOSED WORK VS SOME PREVIOUSLY REPORTED WORK Properties Proposed design
Substrate thickness 1.57
-10 dB, (S11) BW (%) 13.53
Peak gain (dBi) 4.7
[2] [7] [8]
0.5 0.78 1.57
1.8 6.3 11.0
5.3 6.0 6.0
0.78 1.57
10 1.4,5.7
7.5 4.8, 6.1
[11] [14] [15]
4. CONCLUSION
Freq band
,
0.78
9.4 3.8 *Microstrip Line (MSL) **
Feeding topology SIW, MSL MSL MSL MSL MSL MSL, SIW MSL
In this paper, a low-profile broadband planar cavity-backed antenna is presented for Ku-band applications. The proposed antenna uses a modified triangular-ting-slot for radiation. The radiation slot is excited by an SIW feed through the inductive window follows 50 Ω microstrip line for planar integration. The modified triangular-ting-slot on the top cladding induces strong loading effect to the SIW cavity, resultantly, two hybrid modes get excited between TE 110 and TE120 cavity modes. The individual bandwidths of these hybrid modes are in close proximity which leads to a broadband response. The antenna exhibits a measured impedance bandwidth of 13.53% ranging from 14.43~16.49 GHz. The proposed design can be easily rescaled to any desired frequency range by altering corresponding dimensions. The total volume occupied by the antenna, including transition in terms of is 0.77
× 1.63
× 0.07 . Moreover, proposed antenna exhibits unidirectional radiation and
uniform gain characteristics about 4 dBi for the entire operating frequency range, which makes it a promising candidate for broadband applications. REFERENCES 1.
Deslandes D, Wu K. Integrated microstrip and rectangular waveguide in planar form. IEEE Microw. Wireless Compon Lett. 2001;11:68–70.
2.
Luo GQ, Hu ZF, Liang Y. Development of low profile cavity backed crossed slot antennas for planar integration. IEEE Trans Antennas Propag. 2009;57:2972–2979.
3.
Liu Y, Chen S, Ren Y, Cheng J, Liu QH. A broadband proximity-coupled dual-polarized microstrip antenna with L-shape backed cavity for X-band applications. AEU-International Journal of Electronics and Communications. 2015 Sep 30;69(9):1226-32.
4.
Kumar A, Raghavan S. Design of a broadband planar cavity-backed circular patch antenna. AEUInternational Journal of Electronics and Communications. 2017 Dec 1;82:413-9.
5.
Yun S, Kim DY, Nam S. Bandwidth enhancement of cavity backed slot antenna using a via-hole above the Slot. IEEE Antenna Wireless Propag Lett. 2012;11:1092–1095.
6.
Yun S, Kim DY, Nam S. Bandwidth and efficiency enhancement of cavity-backed slot antenna using a substrate removal. IEEE Antenna Wireless Propag Lett. 2012;11:1458–1461.
7.
Luo GQ, Hu ZF, Li WJ, Zhang XH, Sun LL, Zheng JF. Bandwidth enhanced low-profile cavitybacked slot antenna by using hybrid SIW cavity modes. IEEE Trans Antennas Propag. 2012:60:1698–1704.
8.
Kumar A, Raghavan S. Wideband slotted substrate integrated waveguide cavity backed antenna for Ku–band application. Microw Opt Technol Lett. 2017;59:1613–1619.
9.
Sievenpiper D, Hsu HP, Riley RM. Low-profile cavity-backed crossed-slot antenna with a singleprobe feed designed for 2.34-GHz satellite radio applications. IEEE Trans. Antennas Propag. 2004;52:873–879.
10.
Yang W, Zhou J. Wideband low profile substrate integrated waveguide cavity backed E-shaped patch antenna. IEEE Antenna Wireless Propag Lett. 2013;1:143–146.
11.
Dashti H, Neshati MH. Development of low-profile patch and semi-circular SIW cavity hybrid antennas. IEEE Trans Antennas Propag. 2014;62:4481–4488.
12.
Xu JF, Chen ZN, Qing XM, Hong W. Bandwidth enhancement for a 60 GHz substrate integrated waveguide fed cavity array antenna on LTCC. IEEE Trans. Antennas Propag. 2011;59:826–832.
13.
Xu F, Wu K. Guided-wave and leakage characteristics of substrate integrated waveguide. IEEE Trans Microwave Theory Tech. 2005;53:66–73
14.
Zhang T, Hong W, Zhang Y, Wu K. Design and analysis of SIW cavity backed dual-band antennas with a dual-mode triangular ring slot. IEEE Trans Antennas Propag. 2014;62:5007–5016.
15.
Mukherjee S, Biswas A, Srivastava KV. Broadband substrate integrated waveguide cavity-backed bow-tie slot antenna. IEEE Antenna Wireless Propag Lett. 2014;13;1152–1155.
Broadband SIW Cavity-Backed TriangularRing-Slotted Antenna for Ku-Band Applications Author-1: (Corresponding Author) Arvind Kumar Dept. Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620 015 [email protected], contact no. 8903228621
Author-2: Singaravelu Raghavan Dept. Department of Electronics and Communication Engineering, National Institute of Technology (NIT), Trichy, INDIA-620 015 [email protected]